Water soluble polyester coating compositions

Abstract

Water soluble polyester coating compositions convertible to baked coatings characterized by chemical resistance, hardness and flexibility comprising a polyol component incorporating a minor proportion of pentaerythritol and a coupling agent constituted by phthalic anhydride. After neutralizing with a base the water soluble polyester can be interacted with a cross-linking agent, e.g., an aminoplast.

1.  In the production of polyester resins adapted for use in baked coatings comprising reacting at least one polybasic acid with a molar excess of at least one polyol to provide a hydroxy terminated polyester the improvement which comprises incorporating pentaerythritol as an essential element of the polyol component and reacting available hydroxyl groups in the preformed polyester with phthalic anhydride, whereby said polyester is rendered water soluble upon neutralization, and is convertible upon cross-linking to a baked coating characterized by chemical resistance, hardness and flexibility. 
     
     
       2. A process for the preparation of a water soluble polyester resin comprising 1. reacting at least one polybasic acid with a molar excess of at least one polyol, said polyol consisting essentially of a minor proportion of pentaerythritol to form a hydroxy terminated polyester;   2. reacting said polyester with an amount of phthalic anhydride sufficient to provide at least one free carboxyl functionality per 1000 gms; and   3. neutralizing free carboxyl groups in the polyester of step (2) to provide a water soluble polyester resin.   
     
     
       3. The process of claim 2, wherein said polyol comprises pentaerythritol and an aliphatic diol. 
     
     
       4. The process of claim 3 wherein said aliphatic diol is neopentyl glycol. 
     
     
       5. The process of claim 4, wherein the molar ratio of neopentyl glycol to pentaerythritol is in the range of 2:1 to 10:1. 
     
     
       6. The process of claim 2 wherein said polybasic acid comprises an aliphatic and an aromatic dibasic acid. 
     
     
       7. The process of claim 6, wherein said aliphatic dibasic acid is adipic acid and said aromatic acid is isophthalic acid. 
     
     
       8. A polyester resin comprising adipic acid isophthalic acid, neopentyl glycol and pentaerythritol in the approximate molar ratio 3:4:7:2. 
     
     
       9. The polyester resin of claim 8, reacted with about 2 molar proportions of phthalic anhydride. 
     
     
       10. A water-soluble polyester resin comprising the base neutralized product of claim 9. 
     
     
       11. A baked coating comprising the aminoplast cross-linked product of claim 10. 
     
     
       12. A process for the preparation of polyester resin coating compositions comprising reacting at least one polybasic acid with a molar excess of a polyol comprising neopentyl glycol and pentaerythritol in a molar ratio of said pentaerythritol of between about 2:1 and 10:1 to provide a hydroxyl terminated polyester resin having an excess hydroxyl value of 10 to 25%; reacting said hydroxyl terminated polyester with phthalic anhydride to provide a resin with an acid number between about 50 and 60; and neutralizing sufficient carboxyl functionality by reaction with a base to afford water solubility characteristics.